Long Term Evolution (LTE) has emerged as a high-speed and high-capacity radio communication standard. In contrast with predecessor legacy networks that employ a combination of circuit-switching (CS) and packet-switching (PS) for data transmission (such as e.g. GSM/EDGE, UMTS/HSPA, CDMA2000/1×EV-DO, etc.), LTE networks are all-IP networks that exclusively provide on packet-switched transmission.
Despite the improvements offered by LTE over the various legacy networks, many currently-deployed LTE networks may not yet be capable of supporting voice calls (known as Voice over LTE (VoLTE)). Accordingly, while users may enjoy the high data rates of LTE for other packet data uses (such as e.g. Internet access, application data, streaming media, etc.), mobile terminals may need to rely on circuit-switched legacy networks to support voice calls. A mobile terminal may thus need to transition, or “fall back”, to a legacy circuit-switched network in order to both make and receive voice calls. Such procedures are known as Circuit-Switched Fallback (CSFB).